Several deprecated and undocumented "impl_*" methods have been removed from JDK 9.

In prior releases, many public JavaFX classes in exported packages had public or protected implementation methods that were named with "impl_*" in the name, marked as "@Deprecated" with the stated intention of removing them, and hidden from the API documentation with the "@treatAsPrivate" javadoc tag.

These methods were never supported and were not intended to be used by applications. JavaFX applications that were using these undocumented methods will need to stop calling them.